Addition to README - helpful info about tiny-ec2-bootstrap?

Created by: phlummox

I ran into an issue trying to make a new AMI based on the ones provided here (for which, thank you, they are much appreciated!) - I was completely unable to ssh into instances created from the AMI, regardless of what I did.

I eventually discovered the issue was spelled out in the tiny-ec2-bootstrap README: if the tool you use to make a new AMI (packer, in my case) doesn't delete /var/lib/cloud/.bootstrap-complete, then an instance created from the AMI will ignore all attempts at setting a login key...

I wondered if it might be worth mentioning this in the README, since a lot of Amazon's documentation is geared towards AMIs that use cloud-init, so tracking down the issue took a long time.

Thanks again!